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View Full Version : More Holman Moody Volvo Outdrive Questions?



Craig
09-27-2002, 12:07 PM
Noting the other HM Volvo Outdrive entry, I have noticed in my shop manual that the AQ250 had an option for a lower, so I assume faster, gear ratio than the 270 (the 270's best being 1.61:1). Is the reasoning accurate that boats with the 250's are going to be a little faster (all other things being equal)? The old Powerboat Magazine articles (discussed previously) from March 1970 that critiqued the Donzi 18-2+3 and the Cobalt XV-200 (the Donzi 16 copy) detailed both of these boats equipped with a 302 HM Ford and HM outdrive. They call the drive for both simply the "B Unit" (i.e. they don't say 270, etc.) but while they mention that the B unit had 1.61:1 gears, they also mention an available "A Unit" with 1.35:1 gears. I don't think the 270 had that gear option. Did the 250 and 270 overlap in production years? I love the little "Holman Moody Marine" outdrive plates, but it sure is easier to know what old Volvo drive you have if just says 270, 280, etc. on it like "non HM" Volvos!! Anyway, just for fun, here's the performance of the test boats: They both had, as said earlier 302 Fords (235hp), the "B unit" with 1.61:1 gears, a 14x21 medium cupped 3 blade prop (assume aluminum back then) and a Holley 600 CFM carb. Given all that info., they both ran 51 mph at 5000 rpm's and 4700 rpm's respectively. Not as impressive as nowadays, but not too bad for aluminum props! Back to the 250, 270 thing, are those drives fairly interchangeable??